CONSTRUCTION OF HOT-HOUSES. 281 



the height of twelve or fifteen inches, and the arch 

 is turned with the same materials. Fire-clay is 

 used in place of lime. 



The best fuel for the use of the hot-house, is 

 charcoal of pit-coal, as making the most steady fire, 

 the keenest, and the clearest ; and the next best, a 

 mixture of cinders with small coal. Cinders and 

 peat make a good fire, but not very lasting. Wood 

 is the worst, as blazing off too suddenly. Whoever 

 has pit coal at command, may easily char it for his 

 own use, if not sold so at the works ; for uncharred 

 coal should never be used. When the mass of fuel 

 of this kind is fairly lighted, it will last, in a slow 

 soaking state, for twenty-four hours together ; and 

 is always ready to be stirred up when necessity re- 

 quires a brisker heat in the flue ; a matter very dif- 

 ferent from that of lighting a new fire ; but which 

 is a matter of course, with the trifling furnaces al- 

 luded to above. 



Of Flues. 



Many are the opinions respecting the proper di- 

 mensions of flues for the hot-house (I mean fire 

 flues), and the materials of which they should be 

 constructed. I have been at much trouble to sa- 

 tisfy myself of this particular, and have made many 

 experiments with flues of various kinds ; so much 

 having been agitated concerning them of late. I 

 am prepared to say, there is no flue for the use of a 

 hot-house equal to one constructed of brick and 

 tile, thus : 



